Don't take away your own liberties
A common mistake in Go, is taking away your own liberties.
However, after , Black's liberties are reduced from six to five.
As his formation is still open to invasion, reduction or attack, losing a liberty is too high a cost compared to White's cost of 1 point at this stage.
Furthermore, this move loses a ko-threat, but that was not the issue here.
A vain attempt to cut the bamboo joint: White's stones now have three liberties.
This will always be bad (exception if played as a ko threat)
Almost as bad as losing a liberty, is playing but not gaining any liberties.
The exchange - leaves White with three liberties: the same number as she had before. This is one of the ideas behind hane at the head.
After here, whatever Black does, she (White) will end up with at least four liberties for her group.
...because of shortage of liberties, he can no longer play a to make a second eye
A more complex situation where removing one's own liberties gives a bad result: Removing one's own liberties Example 1
tderz: the two examples above are very good as a first instinct reaction ('gain liberties', 'stay ahead', 'play/avoid hane at the head of two'),
but do not necessarily show bad play:
tderz: The exchange - leaves White with three liberties: the same number as she had before. This is one of the ideas behind hane at the head. -> if the surroundings allow and the situation fits, Black may be cut & in a bad/worse situation, as both only have 2 liberties.
tderz: this is espec. good & important if the direction , is the route for escape/attack.
tderz: this is not a perfect example in my view.
tderz: is sente once game is about 11 points/move (23/2) and Black needs to defend with .
tderz: Black's push at can thus also be considered as a good reverse sente,
as it creates a weaknesses (of course, Black has to come back and defend).
Continuations could be a-b-c-d-e or c-(f, h or i) etc.
tderz: perhaps the goup is heavy now and on the left there are imponderabilities as a + b + c.
I certainly prefer defects in opponent's wall + split groups in gote over
being forced to accept a perfect wall in gote.